1. Field of the Invention
The present invention relates to a steering column apparatus of a motor vehicle, and more particularly, to a collapsible steering column apparatus which can absorb and reduce the shock applied to a driver by a steering wheel at the time of a motor vehicle collision.
2. Description of the Prior Art
FIG. 1 is an exploded perspective view of a conventional steering wheel 10 and steering column 20. Steering wheel 10 includes a rim 12 gripped by the driver's hand for steering, a hub 14 for transmitting the rotary force of steering wheel 10 to steering column 20, and a spoke 16 for connecting rim 12 and hub 14. Spoke 16 and rim 12 are internally reinforced by steel or light alloy seam and are externally plasticized with synthetic resin.
Also, in order to reduce the damage against the driver due to the collision of steering wheel 10 and the driver when a motor vehicle collides, hub 14 and spoke 15 are embraced by synthetic resin to widen the contact area with the driver's body.
A vehicle collision involves a so-called primary shock wherein the vehicle collides with another vehicle or the like and a so-called secondary shock subsequently induced wherein the driver strikes against a steering wheel. The secondary shock is applied to the driver's chest or face, the driver is often killed by his neck being broken in the collision of the motor vehicle. Thus, an impact that the driver undergoes upon this secondary shock should be minimized for protecting the life of the driver. A general practice which meets this purpose is that of a so-called collapsible steering shaft which is constructed to reduce the overall length thereof when undergoing a strong impact.
To attain this a collapsible steering column has been developed. A known conventional collapsible steering column apparatus for reducing the secondary shock generated in the collision of the motor vehicle is disclosed in, e.g., U.S. Pat. No. 5,378,021 (Japanese Utility Model Application No. 4-21980) granted on Jan. 3, 1995 to Mikio Yamaguchi et al, which is shown in FIGS. 2 through 4.
FIG. 2 is a view for illustrating Yamaguchi's steering column apparatus 30 using an energy absorbing member 40. FIG. 3 is a sectional view taken along the line A--A in FIG. 2. FIG. 4 is a view illustrating energy absorbing member 40 used in FIGS. 2 and 3.
As shown in FIGS. 2 and 3, Yamaguchi's collapsible steering column apparatus 30 includes a steering column 22 into which a steering shaft 26 and energy absorbing member 40 are inserted. A steering wheel 10 is fixed to the front end of steering shaft 26. A rear end 42 of energy absorbing member 40 is fixed to the outer peripheral surface of steering column 22 and a front end 46 thereof is connected to a support bracket 24 fixed to a vehicle body 52 by a bolt 48 and a nut 50.
Energy absorbing member 40 is manufactured by punching out a sheet of metal plate and has a laterally undulating configuration 44.
If a force (F) of the direction shown in FIG. 2 is applied to steering column 22 by the secondary shock generated at the time of collision, steering column 22 moves lengthwise. At this time, energy absorbing member 40 whose rear end 42 is supported to the outer peripheral surface of steering column 22 and whose from end 46 is connected to support bracket 24, is collapsed lengthwise and is elongated laterally by the force (F), as shown in FIG. 4 (the upward and downward arrow directions).
The force necessary for arising the elongation of energy absorbing member 40 is not greatly increased. Ultimately, the forward displacement of steering column 22 is smoothly started. While the forward displacement of steering column 22 progresses, energy absorbing member 40 is collapsed lengthwise and is elongated laterally to then absorb the force (F).
Further, since energy absorbing member 40 has undulating configuration 44, as shown in FIG. 4, the lateral elongation of undulating configuration 44 of energy absorbing member 40 decreases progressively. The force necessary for causing the elongation of energy absorbing member 40 is comparatively small at the initial stage but the force necessary for causing further lateral elongation gradually should be larger than that of the initial stage along with a progression of the elongation of energy absorbing member 40. Therefore the displacement of energy absorbing member 40 decreases gradually so that the forward movement of steering column 22 becomes small gradually.
As described above, Yamaguchi's collapsible steering column apparatus 30 absorbs the impulsive force of the vehicle by energy absorbing member 40 to reduce the shock transmitted to the driver.
However, Yamaguchi's collapsible steering column apparatus 30 cannot prevent the movement of steering column 22 toward the driver. Since energy absorbing member 40 is plastically deformed, it is not reusable and should be replaced with a new one after its use. Also, since steering wheel 10 is made of steel, when the driver's body strikes against steering wheel 10 at the time of collision, the driver's body may receive a serious shock.